Emission controls for internal combustion engines have become increasingly important as concerns over environmental damage and pollution have risen prompting legislators to pass more stringent emission controls. Much progress has been made in improving exhaust emission controls. However, crankcase emission controls have been largely neglected.
Crankcase emissions result from gas escaping past piston rings of an internal combustion engine and entering the crankcase due to high pressure in the cylinders during compression and combustion. As the blow-by gas passes through the crankcase and out the breather, it becomes contaminated with oil mist. In addition to the oil mist, crankcase emissions also contain wear particles and air/fuel emissions. Only a small number of heavy diesel engines have crankcase emission controls. Some of current production diesel engines discharge these crankcase emissions to the atmosphere through a draft tube or similar breather vent contributing to air pollution. Some of the crankcase emissions are drawn into the engine intake system causing internal engine contamination and loss of efficiency.
The released oily crankcase emissions coat engine sites, such as the inside of engine compartments or chambers, fouling expensive components and increasing costs, such as clean-up, maintenance and repair costs. As the oily residue builds up on critical engine components, such as radiator cores, turbocharger blades, intercoolers and air filters, it becomes a "magnet" for dust, grit and other airborne contaminants. Particulates in the contaminated oily crankcase emissions include particles and aerosols. The accumulation of the particulates on these components reduces efficiency, performance and reliability of the engine.
In addition to increasing engine performance and decreasing maintenance intervals and site/critical engine component contamination, crankcase emission controls are becoming increasingly important in reducing air pollution. Engine emissions include both crankcase and exhaust emissions. Because of reductions in exhaust emissions, the percentage of the total engine emissions due to crankcase emissions has risen. Therefore, reducing crankcase emissions provides a greater environmental impact with engines having low exhaust emissions.
Furthermore, most of the crankcase particulate emissions (CPE) are soluble hydrocarbons, as opposed to the exhaust emissions that are mainly insoluble organics. The crankcase particulate emissions are oil related, with ethylene (C.sub.2 H.sub.4) being predominant. Therefore, separating the oil and returning the cleaned oil free crankcase emissions to the engine inlet for combustion increases engine efficiency.
Crankcase flow and particulate emissions increase dramatically with engine life and operating time. Thus, the environmental impact and engine efficiency from recycling the crankcase emissions increase with operating time. For example, in buses having diesel engines, the crankcase particulate emissions represent as much as 50% of the total exhaust particulate emissions.
Crankcase emission control systems filter the crankcase particulate emissions and separate the oil mist from the crankcase fumes. The separated oil is collected for periodic disposal or return to the crankcase.
Crankcase emission control systems may be "open" or "closed" systems. In open crankcase emission control systems, the cleaned gases are vented to the atmosphere. Although open systems have been acceptable in many markets, they pollute the air by venting emission to the atmosphere and can suffer from low efficiency. Closed systems eliminate crankcase emissions to the atmosphere, meet strict environmental regulations, and eliminate site and external critical component contamination.
In closed crankcase emission control systems, the cleaned gases are returned to the engine combustion inlet. One of the first closed systems by Diesel Research, Inc. of Hampton Bays, N.Y., included a two-component crankcase pressure regulator and a separate filter.
Closed crankcase emission control systems require a high efficiency filter and crankcase pressure regulator. The high efficiency filter is required to filter out small sized particles to prevent contamination of turbochargers, aftercooler, and internal engine components. The pressure regulator maintains acceptable levels of crankcase pressure over a wide range of crankcase gas flow and inlet restrictions.
In a closed system, the crankcase breather is connected to the inlet of the closed crankcase emission control system. The outlet of the closed crankcase emission control system is connected to the engine air inlet, where the filtered blow-by gas is recycled through the combustion process.
A recent improvement to closed crankcase emission control systems is shown in U.S. Pat. No. 5,564,401, which is also owned by Diesel Research, Inc. In this system, a pressure control assembly and a filter are integrated into a single compact unit. The pressure control assembly is located in a housing body and is configured to regulate pressure through the system as well as agglomerate particles suspended in the blow-by gasses. Inlet and outlet ports direct the blow-by gasses into and out of the housing body from the engine block. A filter housing enclosing a replaceable filter is removably attached to the housing body to separate any remaining oil from the blow-by gasses. The filter element can be easily removed from the filter housing for replacement, after removing the filter housing from the housing body. The separated oil drains down and collects in a reservoir at the bottom of the filter housing. An oil drain check valve is located in the bottom wall of the filter housing, and includes a free-floating (one-way) valve. The check valve is connected through a separate return line to the oil pan or engine block to return the collected oil to the engine.
The system shown in U.S. Pat. No. 5,564,401 provides a closed crankcase emission control systems that is compact and combines various components into a single integrated unit, is efficient, and is simple and inexpensive to manufacture.
Nevertheless, it is believed there are certain disadvantages to the '401 emission control system. The oil collecting on the inside surface of the media ring drains down onto the lower end cap, and then must make its way radially outward through the media, before it then drips down into the oil reservoir area for return to the engine. The return path through the media can be obstructed as the filter element becomes spent, which results in the oil being retained in the element and thereby less oil being returned to the engine crankcase. Spillage of the oil can occur during an element change, which can create handling issues.
The filter element in the '401 system may also be removed and replaced with less-preferred elements. This is because the filter element in the '401 patent comprises a simple, ring-shaped media with a pair of end caps, which is available from a number of sources. However, less-preferred elements can suffer from poor performance, incorrect sizing, inappropriate material, etc. Replacing an approved filter element with a less-preferred element can reduce the oil-separating ability of the filter and, in extreme circumstances, possibly harm the engine.
The check valve in the housing for the '401 system can also become clogged and/or worn over time, and have to be removed and replaced. Since the check valve is part of the filter housing, this generally means replacement of the entire (relatively expensive) filter housing, and also keeping a separate maintenance schedule for the filter housing/check valve.
Still further, the return line for the oil is a separate component from the crankcase emission line from the engine. This requires separate plumbing between the engine and emission control system, and generally increases the material, installation and maintenance costs associated with the system.
While the system shown in the '401 patent has received considerable acceptance in the market as being a considerable improvement over previous systems, it is believed there is a demand in the industry for a further improvement, most notably an improved filter assembly for such a crankcase emission control system which overcomes the drawbacks noted above, and still provides a system that is compact and combines various components into a single integrated unit, is efficient, and is simple and inexpensive to manufacture.